Sucker rod pumps are used throughout the entire industry and are adapted for pumping various kinds of liquids. These pumps are also very popular in oil well production and cover a large percentage of oil wells on artificial lift worldwide. There are three basic types of constructions like insert pumps, tubing pumps and casing pumps.
However, the pump principle is similar for the three different pump types. In such pump devices, in particular in sucker rod pumps, a pump is actuated in a defined depth by the sucker rod string which is hence reciprocated by a beam pumping unit at the surface. The pump is basically composed of a pump plunger that is movably supported in the bore hole and that comprise a travelling valve. At the bottom of the bore hole a pump barrel is installed that includes a standing valve.
During an upstroke of the pump, the plunger is lifted together with the entire column of liquid that is gathered in the bore hole above the plunger. The travelling valve at the lower end of the pump plunger is therefore closed and hinders the liquid column to flow back at the bottom of the bore hole. At the same time the standing valve of the pump barrel is open and allows fluid to fill the pump.
During a downstroke the standing valve of the pump is closed while at the same time the travelling valve opens in order to make all the fluid in the pump flowing through the plunger above into a tubing string.
Thus, the sucker rod string is under tension during the upstroke due to the lifting of the plunger and thus the lifting of the fluid. During the downstroke, the plunger is pushed downwards by the self weight of a sucker rod and therefore the sucker rod is under compression. Due to this compression of the sucker rods, string buckling of the sucker rods may be caused which results in higher friction and wear of the surrounding tubing so that eventually the entire production from the well may be disturbed.
U.S. Pat. No. 4,049,365 discloses an oil well pump with plunger pull-down and descending assembly. One embodiment involves a tension member that extends downwardly below the plunger so that this tension member keeps the plunger under tension without applying compressive force to the pump rod or sucker rod. An embodiment of the pump provides a weight attached to the bottom of the plunger.